The present invention relates to a ceramic substrate for use in the semiconductor industrial field, and more particularly, it relates to a ceramic substrate for use in a wafer prober, an electrostatic chuck, a hot plate and the like, for use in the manufacture or inspection processes of semiconductors.
Applied semiconductor products are indispensable in many industrial fields. As a typical example, semiconductor chips are manufactured by slicing a silicon monocrystalline to a predetermined thickness to produce a silicon wafer; then forming a variety of circuits in a pattern shape thereon.
In order to manufacture a semiconductor chip, an electrostatic chuck for supporting a wafer, a hot plate for heating a wafer, and a wafer prober for checking whether the circuit operates in accordance with its design are needed. These may preferably be of ceramic material in terms of heat resistance and corrosion resistance.
For example, Japanese patent registration No. 2798570 discloses an electrostatic chuck made of ceramic materials having such construction as to have a heat generation body therein.
FIG. 11 is a cross sectional view showing an example of such electrostatic chuck schematically. The electrostatic chuck shown in the figure is provided therein with a RF electrode 80 and a heat generation body 82. Furthermore, the electrostatic chuck is provided therein with through-holes 84, 86 for connection respectively with the RF electrode 80 and the heat generation body 82. In fact, respective through-holes 84, 86 are formed by a sintered ceramic body of a laminated structure, which have a cylindrical shape, and being filled with conductive components. As the conductive materials, for example, tungsten is adopted. The structure of the through-holes of the electrostatic chuck are such that the electric wiring of respective layers are drawn out and/or connected to each other via an external terminal pins 88.
Accordingly, the through-holes 84, 86 are made of different materials from a sintered ceramic material from the view point of structural metallography. Additionally, a thermal expansion rate of the through-holes 84, 86 is different from that of a sintered ceramic materials. Accordingly, adhesion between tungsten and sintered ceramic materials tends to deteriorated.
Due to a long-term use, if a heat sink cycle and a thermal shock are applied to such electrostatic chuck, adhesion between the through-hole and a sintered ceramic material deteriorates. The external terminal pin is connected using a flux. The structure arises a problem such that the repeated attachment and detachment between the external terminal pin and a power supply causes a drawing force to be applied to the through-hole, thus resulting that adhesion between a through-hole and a sintered ceramic material to be deteriorated.
Such problem is not always brought to an electrostatic chuck, but also to a wafer prober having a ceramic substrate provided with electrodes therein and to a ceramic heater having a ceramic substrate provided with a heat generation body therein.
The object of the present invention is to provide a ceramic substrate which is provided with a through-hole having an excellent tolerance against a drawing stress applied to an external terminal pin, the ceramic substrate being for use in an inspection device for use in processes of manufacturing semiconductors.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a ceramic substrate, which comprises a conductor layer on the surface or inside of the ceramic substrate, and a through-hole connected electrically to the conductor layer, wherein a projection is formed on a side wall of the through-hole so as to protrude into said ceramic substrate.
The ceramic substrate for use in an inspection device for use in processes of manufacturing semiconductors has a projection which protrudes into the ceramic substrate, thus allowing remarkable increasing of the adhesion area between the conductor materials for use in forming through-holes and the ceramic substrate. Furthermore, the projection has an anchor effect, thus allowing adhesion between them to be increased. Accordingly, such adhesion allows the ceramic substrate of the present invention to have an excellent tolerance against a drawing stress applied to an external terminal pin fixed to the through-hole""s end face.
In this case, the conductor layer may satisfactorily be formed on the surface and the through-hole which is electrically connected to the conductor layer may satisfactorily be formed on the ceramic substrate. Thereby, the ceramic substrate may be made to function as a wafer prober.
Alternatively, the ceramic substrate may be made to function as a heater if a heat generation means is formed as a conductor layer inside the ceramic substrate, and if the through-hole being connected to the conductor layer is formed on the ceramic substrate, furthermore, a projection is formed on a side wall of the through-hole so that the projection may protrude into the ceramic substrate.
In accordance with the ceramic substrate having above identified structure, the projection (or protrusion) from the through-hole which functions as a heat conduction radiates heat, thus allowing uniformity of heating over the entire ceramic substrate to be improved. If a through-hole with no projection is connected to a heat generation body then a heat conductivity of a ceramic material under a high temperature may decrease, thus resulting a heat concentration on the through-hole. This part becomes a specific point (a hot spot) which is a cause of a damage of a semiconductor wafer. In contrast, according to the present invention, there is no heat concentration on a through-hole because the projection of the ceramic substrate also functions as a cool-down fin. Such ceramic substrate can be incorporated into devices which needs the heat controls, such as a wafer prober or an electrostatic chuck. The ceramic substrate may be used under a temperature from 150 to 1800xc2x0 C. depending on its application.
Alternatively, an electrostatic electrode as a conductor layer may be provided for inside of the ceramic substrate, and through-hole being connected electrically to the electrostatic electrode may be formed on the ceramic substrate, then a projection may be formed on a side wall of the through-hole so that the projection may protrude into the ceramic substrate. Thereby, the ceramic substrate may be made to function as an electrostatic chuck. Where, xe2x80x9can electrostatic chuckxe2x80x9d is an electrode which attracts a semiconductor wafer by means of an electrostatic force under voltage.
As the material used for xe2x80x9cthe ceramic substratexe2x80x9d according to this invention, a sintered substrate of aluminium nitride may be preferable. The material used for the ceramic substrate is not limited to aluminium nitride. For example, other ceramic materials may also be equally used instead, such as carbide ceramics, oxide ceramics, nitride ceramics except aluminium nitride and the like.
Some examples of xe2x80x9ccarbide ceramicsxe2x80x9d include, by way of examples not limitative, metal carbide ceramic material such as silicon carbide, zirconium carbide, titanium carbide, tantalum carbide, tungsten carbide and the like. Some examples of xe2x80x9coxide ceramicsxe2x80x9d include, by way of examples not limitative, metal oxide ceramic material such as alumina, zirconia, cordierite, mullite and the like. Some examples of xe2x80x9cnitride ceramicsxe2x80x9d include, by way of examples not limitative, the metal nitride ceramic material such as silicon nitride, boron nitride, titanium nitride and the like, other than the aluminium nitride as described above. Among these ceramic materials, in general, nitride ceramics and carbide ceramics are preferred to oxide ceramics because of their heat conductivity. The sintered bodies may be of a single material or of a plurality of materials.